1. Field of the Invention
This invention relates to a semiconductor light emitting device and a method for manufacturing the same, and an epitaxial wafer.
2. Background Art
A light emitting device emitting visual light, such as green, yellow-green, yellow, orange, and red, has been widely used in such applications as lighting apparatus, car-use lighting equipment, display device, traffic signal, and so on. If a light emitting device can be brighter, outdoor applications can extend, and also low consumption power becomes possible due to a reduction of an operating current.
If a light emitting layer of the semiconductor light emitting device is formed on a GaAs substrate having band gap wavelength of approximately 870 nm longer than that of a visual light wavelength range of green to red, a radiant light toward the GaAs substrate is absorbed and an optical output power is reduced.
On the contrary, if a GaP substrate having a band gap wavelength of 550 nm shorter than that of visual light wavelength range of yellow-green to red is used, the absorption in the GaP substrate is reduced and high intensity becomes possible.
However, because a lattice constant difference between InGaAlP-based base semiconductor which emits visual light having a wavelength range of yellow-green to red and GaP material is approximately several percents, it is difficult that a laminate body, made of InGaAlP, having low crystal defect density is directly grown on the GaP substrate.
There is disclosed a technique which provides a light emitting device having high light emitting efficiency while avoiding undesirable influence to light emitting portion due to heat treatment in wafer bonding process (JP-A 2001-144322 (Kokai)). In this disclosure example, there is disclosed a method for manufacturing a semiconductor light emitting device comprising; growing a first semiconductor layer on a first substrate in a lattice fitting state, detaching the first substrate after bonding the first semiconductor layer and a second substrate, and growing a second semiconductor layer on the first semiconductor layer bonded to the second substrate. In this case, a lattice misfit can be relaxed because the first semiconductor layer is provided.
However, when the first semiconductor layer is made of InGaAlP based material, its surface tends to be unstable, and therefore, crystal defect density tends to be higher.